The use of photovoltaic systems, which convert incident sunlight into electrical energy, has become increasingly popular in recent years. The development of more efficient solar cells, as well as the lower production costs realized in the manufacture of continuously deposited, amorphous solar cells, has made such power systems more practical. For example, photovoltaic modules are being used to power devices such as radios, to trickle charge batteries in parked cars, and in night illumination systems.
Of course, it would also be useful to employ photovoltaic power to operate electric motors such as, for example, electric fans, refrigerators, hot water pumps, etc. However, one problem which arises when employing photovoltaics to operate electric motors results from the relatively high currents which must be used to start the typical electric motor, even a relatively small one. Thus, prior art photovoltaic power systems, while perfectly capable of providing enough current to run an electric motor, once started, are generally not sufficient to get the motor up and running. On the other hand, a power module which has sufficient capacity to start a motor will have a capacity far exceeding that needed to sustain operation of the motor. This excess capacity represents a loss in terms of material and space.
Of course, there have been some attempts in the prior art to solve this problem by employing such devices as accumulators, storage batteries and electronic sensing devices. U.S. Pat. Nos. 4,483,319 and 4,614,879 illustrate solar power supply systems for situations requiring a starting current which is higher than a minimum running current. In particular, the '319 patent discloses a circuit for starting a pump motor to operate a solar hot water system; the circuit includes a capacitor disposed between the photovoltaic panel and the pump. The pump is isolated from the capacitor until the voltage on the capacitor reaches a level sufficient to start the pump motor. The '879 patent discloses the use of an electronic regulator for adjusting panel output to provide for motor starting. U.S. Pat. No. 4,100,427 shows a photovoltaic power system employing a plurality of electric accumulators in the form of batteries which are connected to a plurality of photo cells. A switching means is provided for connecting a load to the photo cells only so that load current is determined by the photo cell current during the starting period of the load.
All known prior art systems suffer from one or more problems such as undue complexity, energy inefficiency, and unreliability. Clearly, there is a need for a photovoltaic power module which may be used to start and run an electric motor, which is reliable, simple in operation, and which makes efficient use of the energy generated. The present invention is directed to such a system.